Saintly writers of the first centuries of the Christian era, whom the Catholic Church acknowledges as witnesses of her faith. There are four qualities are required of a writer to be numbered among the Fathers of the Church

Though the majority of the Fathers were bishops, yet this is not true of all of them. SaintJerome was a simple priest to the end of his days, Saint Ephraem a deacon, Saint Justin a layman. Not all Fathers have been proclaimed Doctors of the Church. In matters of faith and morals, the consent of the Fathers has always been held in high esteem by the Church. What they unanimously teach to be of faith, is of faith; what they unanimously reject as heretical, is heretical. Even the logical conclusions which they unanimously draw from the articles of faith, furnish us with a certain theological argument. Their authority is due not only to the fact that they were saints or bishops or eminent scholars and lived at a time when Christ’s revelation was still fresh in the minds of men, but primarily to the approbation of the Church. What Christ said of the Apostles, “He that heareth you heareth me”, the Church says in a manner of the Fathers. They are the mouthpiece of the infallible teaching body of the Church, and the Church acknowledges them as witnesses of her own faith. Hence, when anathematizing new heresies or defining new dogmas, the Councils appeal to the consent of the Fathers. The Council of Ephesus in 431 declared in its first session that it would define nothing save what had been held unanimously by the ancient and holy Fathers. This approbation of the Church gives added authority even to the Fathers, considered singly, though in varying degrees. A general approbation given to a saintly writer of the first centuries implies that his doctrine in general is orthodox and worthy of recommendation. Sometimes, however, a certain Father’s doctrine receives a special approbation as being exceptionally solid; such is SaintAugustine‘s fundamental doctrine on grace. Lastly, the highest degree of ecclesiastical approbation is reached when the Church takes the very doctrine of a Father and embodies it in her own official pronouncements, as, in the case of SaintCyril of Alexandria, whose twelve anathematisms against Nestorius were adopted by the Council of Ephesus.